The present invention relates to atomic spectrometry and more particularly to apparatus for inductively coupled plasma spectrometry and the like.
In spectroscopic analysis of the alkali elements (sodium-Na, lithium-Li, potassium-K, cesium-Cs and rubidium-Rb), non-linearities are exhibited which can lead to significant inaccuracies in analysis. These non-linearities usually manifest themselves in two ways. First, the signals produced by each element in solution do not correlate linearly with increases in their concentration. Second, for a given concentration of an alkali element, e.g., Na, changes in the concentration of the other alkali elements, e.g., K, alter the Na signal. These non-linear effects (known as easily ionizable element or "EIE" effects) are believed due to the relatively low electron density of the plasma and the relatively cool temperature of both the preheating zone and the tail plume of the plasma.
In conventional plasma imaging systems for spectroscopic analysis, the plasma is viewed axially. Since the plasma axis is coincident with the optical viewing axis of the spectrometer, the entire plasma is observed. This includes the preheating zone and the tail plume where matrix interferences or EIE effects are pronounced. While conventional axial viewing systems have been noted for their detection limits, sensitivity, precision and reduced background signal interference, EIE effects persist leading to significant inaccuracies in spectroscopic analysis.